1. Field of the Invention
The present invention relates to a three-phase common tank type gas circuit breaker and, more particularly, to a three-phase common tank type gas circuit breaker used in a large power system such as of 550 KV and which has single-break closing resistors and capacitors.
2. Description of the Prior Art
Power systems of high voltage and large capacity are becoming a matter of great concern in view of the recent increasing demand for electrical power. This has given a rise to a demand for increased capacities of circuit breakers, used in substations to break greater powers of higher voltages. Circuit breakers also are required to have a reduced number of breaks as well as to cope with the increase in the power to be broken, in order to attain an improved braking performance. More specifically, dual break type circuit breakers capable of breaking 50 KA current, usable in 550 KV line for example, have been put in practical use. However, a demand exists for single break circuit breaker of the same class as above. This applies also to the case of gas-insulated circuit breakers. For example, in Japanese Patent Unexamined Publication No. 2-46616 a single break circuit breaker, a so-called three phase common tank type gas circuit breaker, is proposed wherein, interrupters for three phases are accommodated by a common hermetic tank so as to reduce the size of the entire gas-insulated circuit breaker.
In this circuit breaker, in order to deal with an electric line of a large capacity of the order of 550 KV, a closing resistor for limiting closing switching overvoltage and a capacitor for limiting transient recovery voltage are disposed in parallel with the interrupter of each phase.
In the prior art described, the circuit breaker has a grounded tank and three-phase assemblies for the three phases of the power accommodated in the grounded tank, with each assembly having an interrupter, a closing resistor and a capacitor connected in parallel with the interrupter. More specifically, the closing resistors are disposed on the radially inner side of the interrupters and the capacitors are disposed in the central region of the grounded tank, with the closing resistors and the capacitors being shielded by a cylindrical shield member. Single break function requires that one interrupter is associated with a capacitor which corresponds in capacitance to those used for conventional dual break type breakers. In addition, circuit breakers for use in such a large power line as of 550 KV class require closing resistors which have a length of about one meter and which are connected in series. The arrangement of the closing resistors in the prior art circuit breaker, therefore, cannot provide a compact circuit breaker because the dimensions of the circuit breaker tend to be increased due to large axial dimensions of the closing resistors.